Systems employing optical data storage locations include, for example, video cameras and image displays. Such systems employ an addressing structure that provides data to or retrieves data from the storage locations. One system of this type is a general purpose flat panel display, whose storage or display locations store light pattern data. A flat panel display comprises multiple display locations distributed throughout the viewing area of a display surface.
One type of flat panel display system employs a matrix-type addressing structure that accomplishes direct multiplexing of multiple liquid crystal cells that are arranged in an array and function as the display locations. Each of the liquid crystal cells is positioned between a pair of electrical conductors that selectively apply select and deselect voltage signals across the liquid crystal cell to change its optical properties and thereby change the brightness of the image it develops. A display system of this type is characterized as "passive" because no "active" electronic device cooperates with the liquid crystal cell to modify its electro-optical properties. Such a display system suffers from the disadvantage of being capable of implementation in only a low resolution display application having a limited number of addressable lines (i.e., up to about 250) of video information or data for developing a display image. Such a display system may also suffer from the disadvantages of providing limited gray scale, relatively low image contrast, and a small range of viewing angles.
Another type of flat panel display system having a matrix-type addressing structure employs an array of electrically "active" elements that act as electronic switches at each of the display locations. Such a display system may employ, for example, thin film transistors (TFT) having nonlinear signal processing characteristics that cooperate with the liquid crystal material to provide a full gray scale capability. Such a display system is capable of providing high resolution displays, good image contrast, and relatively wide range of viewing angles. A display system of this type suffers, however, from the disadvantage of being very difficult to fabricate with high production yields because of the large number of electronic elements and data drivers required in such a system. For example, a 1,000 line full color display system of this type could require up to about 3 million electronic elements and about 4,000 data drivers.
Yet another type of flat panel display system is characterized as a flat cathode-ray tube. Such a display system is described in Lamport et al., "The Channel Electron Multiplier CRT: Flat Deflection System," SID 82 Digest. 210-211.
FIGS. 1 and 2 are respective cross sectional and frontal views of a flat cathode-ray tube display system 10 of the type described by Lamport et al. Display system 10 includes an electron gun 12 centrally positioned at the bottom of a back side 14 (FIG. 1) of the display system. Electron gun 12 generates a conventional cylindrical electron beam 16 that is shown propogating along multiple exemplary beam paths. The beam current of electron beam 16 changes in response to luminance information carried by image data or information developed by display system 10.
Electron gun 12 directs beam 16 upwardly in a y-axis direction along back side 14 to a trough-shaped reversing lens 18, which directs the beam around the upper end of a central plate 20 and downwardly in the y-axis direction along a front side 22 of the display system. Electron beam 16 is deflected in an x-axis direction (out of the plane of the page in FIG. 1) by a pair of conventional deflection plates 24 positioned near electron gun 12. Electron beam 16 is deflected in a z-axis direction (out of the plane of the page in FIG. 2) and strikes a display screen 26 successively at different locations spaced apart by a predetermined distance in the y-axis direction. This is accomplished by successively applying voltages of appropriate character to corresponding ones of multiple frame deflection plates 28 that extend in the x-axis direction across the front surface of central plate 20. Display screen 26 includes a channel electron multiplier 30 that receives the deflected electron beam 16 and delivers an increased number of electrons to a fluorescent screen 32 to form on screen 32 a display image corresponding to the image information carried by electron beam 16.
In operation, electron beam 16 is deflected in the x-axis direction by deflection plates 24 to form horizontal scan lines that extend in the x-axis direction across display screen 26. Electron beam 16 is deflected onto display screen 26 at different positions along the y-axis direction by successively switching different ones of the frame deflection plates 28 between a cathode potential of zero volts and an anode potential of about +400 volts, thereby to effect a scanning of different horizontal lines. Accordingly, deflection plates 24 and frame deflection plates 28 cooperate to scan the information-carrying electron beam 16 across display screen 26 in a raster pattern. Electron beam 16 and deflection plates 24 and 28 function, therefore, as an addressing structure for addressing each one of multiple picture elements on display screen 26.
The resolution of display system 10 is determined by the spot size and, therefore, the focusing of electron beam 16 on display screen 26. The electric fields generated by frame deflection plates 28 cooperate to focus electron beam 16 in the y-axis direction as the beam strikes display screen 26, thereby providing display system 10 with relatively high resolution qualities in the y-axis direction. Electron beam 16 is focused in the x-axis direction, however, by means of focusing electrodes included in electron gun 12. Such focusing electrodes are disadvantageous because they are of relatively complex design to compensate for the extreme differences in the electron beam path length at the top and bottom of display screen 26. Display system 10 also suffers from the disadvantage of positioning electron beam 14 in raster scan fashion, which requires that both back side 14 and front side 22 provide electron beam paths of sufficient lengths to scan electron beam 16 over the entire surface of display screen 26. This is disadvantageous because sides 14 and 22 make display system 10 relatively thick and require the reversing lens 18 to direct beam 16 around the end of central plate 20. Increased thickness is an undesirable characteristic of a flat panel display, and reversing lens 18 can degrade the focus of beam 16 in the x-axis direction.